Alli is the only over-the-counter weight loss pill approved by the FDA, making it the best-supported option available without a prescription. Everything else on store shelves, from green tea extract to garcinia cambogia, is classified as a dietary supplement, meaning it hasn’t been rigorously tested or approved for weight loss. That distinction matters more than most people realize.
Alli: The Only FDA-Approved OTC Option
Alli (pronounced AL-eye) contains a 60-milligram dose of orlistat, a drug that works by blocking your intestines from absorbing a portion of the fat you eat. That unabsorbed fat passes through your body instead of being stored. A stronger 120-milligram version is available by prescription under the brand name Xenical, but the OTC dose still produces meaningful results.
Alli is approved for adults 18 and older with a BMI of 25 or more. It’s designed to be used alongside a reduced-calorie, lower-fat diet, not as a standalone solution. The pill works only on the fat in your meals, so it won’t do much if your diet is already low in fat or if excess calories are coming from sugar and carbohydrates.
How Much Weight You Can Expect to Lose
Clinical trials give a realistic picture of what Alli delivers. In one large randomized trial of 635 patients starting at an average weight of about 220 pounds, participants taking the 60-milligram OTC dose lost an average of 7.1% of their body weight over one year, compared to 4.1% with a placebo. A second trial showed even stronger results: 8.6% body weight loss with the OTC dose versus 6.6% with placebo.
In practical terms, that means Alli typically helps you lose roughly 3 to 5 extra pounds over a year beyond what diet alone would achieve. At the six-month mark, one trial found people on the OTC dose had lost about 9.7 pounds compared to 4.6 pounds with placebo. These numbers are modest, but they’re real and reproducible. For context, prescription weight loss medications like phentermine tend to produce higher satisfaction rates (82% of users reporting positive effects, versus 64% for orlistat), but phentermine requires a prescription and carries stimulant-related risks.
Side Effects of Alli
Because Alli works by preventing fat absorption, the most common side effects are gastrointestinal and directly tied to how much fat you eat. When unabsorbed fat passes through your digestive system, you can experience oily or fatty stools, oily spotting on underwear, gas with oily discharge, frequent or hard-to-control bowel movements, and stomach pain. These effects tend to be worst in the first few weeks and improve as your body adjusts and you learn to keep meals lower in fat.
The simplest way to minimize these side effects is to keep each meal under about 15 grams of fat. Eating a high-fat meal while taking Alli will almost certainly cause noticeable digestive issues. Many people find this built-in consequence actually reinforces better eating habits. Because the drug can also reduce absorption of fat-soluble vitamins (A, D, E, and K), taking a daily multivitamin at bedtime, at least two hours after your last dose of Alli, is a good idea.
Popular Supplements That Lack Strong Evidence
Walk down the supplement aisle and you’ll see dozens of products marketed for weight loss. None of them have FDA approval for that purpose, and most have underwhelming clinical data.
Garcinia cambogia is one of the most heavily marketed natural weight loss ingredients. It contains hydroxycitric acid, which is thought to suppress appetite and lower blood fat levels. Some animal studies show reduced triglyceride levels, but clinical results in humans have been inconsistent. One study administering the extract to mice on a normal diet found it lowered blood fat levels but produced no significant change in body weight. The appetite-suppressing effects reported in some trials haven’t been reliably replicated.
Glucomannan, a soluble fiber derived from the konjac plant root, has slightly better evidence. It absorbs water and expands in your stomach, which can help you feel full longer and slow gastric emptying. A meta-analysis of randomized controlled trials found that glucomannan supplementation led to an average weight loss of about 2.1 pounds more than placebo. That’s a real effect, but a small one. The studies also varied widely in dosage, duration, and quality, so the optimal amount to take isn’t well established.
Green tea extract and caffeine are frequently combined in “fat burner” supplements. Caffeine can temporarily increase metabolic rate, and green tea contains compounds called catechins that may enhance fat oxidation. But systematic reviews have found the effects on actual body weight and waist circumference to be minimal or inconsistent. Any calorie-burning boost from these ingredients is small enough that an extra handful of chips would cancel it out.
Conjugated linoleic acid (CLA) has been studied in both animal and human trials, but evidence for meaningful weight loss in people remains limited. Some studies suggest it may modestly reduce body fat percentage, but the effect is small and inconsistent across trials.
The Contamination Problem With Supplements
Beyond weak evidence, there’s a more serious concern with unregulated weight loss supplements. The FDA maintains an active, regularly updated list of weight loss products found to contain hidden, dangerous ingredients. These products are sometimes marketed as “natural” or “herbal” but actually contain undisclosed pharmaceutical drugs, including banned stimulants and other substances that can cause serious cardiovascular problems.
The FDA warns that many diet pills, fat-burning supplements, and weight loss teas sold online or through social media are contaminated with hidden ingredients. These products often have glowing reviews and professional-looking marketing, making them hard to distinguish from legitimate supplements. They can lead to severe health issues and hospitalization. If a supplement promises dramatic results or sounds too good to be true, that’s a red flag. Legitimate supplements produce modest effects at best.
How OTC Options Compare to Prescriptions
The gap between OTC and prescription weight loss medications has widened considerably in recent years. Newer prescription options, including injectable medications that mimic gut hormones, can produce weight loss of 15% or more of body weight. Even older prescription stimulant-based medications outperform Alli by a significant margin. Phentermine, for example, has an 82% positive-experience rate among users compared to 64% for orlistat.
Alli remains the best OTC option because it’s the only one with FDA approval and consistent clinical trial data behind it. But “best available without a prescription” is a different claim than “highly effective.” If you have a BMI of 30 or higher, or 27 or higher with weight-related health conditions, talking to a provider about prescription options will likely give you access to more effective tools. Alli works best as a modest boost for people making real dietary changes, not as a primary weight loss strategy on its own.